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Old 02-06-2009, 03:28 AM #1
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Default quick help with dummy load

Just got my driver built (daedal) and built the dummy load (4diodesand 10hmres). Built just like the pics showed. My problem is that if you check the diodes and resistors you get nothing on the meter. But if you switch the polarity I get the proper measurements. Something isnt right. Or are you supposed to have reverse diodes. Help please. MIKE


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Old 02-06-2009, 07:16 AM #2
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Default Re: quick help with dummy load

Diodes are a bit like one way valves, so everything is fine, if you have built the full DDL circuit you have a diode that will not conduct if the batteries are in correctly and the LD will light, if you put the batteries the wrong way round the power will flow through the diode and not the LD. The same applies to the dummy load, one way nothing happens, the other way current flows.

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Old 02-06-2009, 06:28 PM #3
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Default Re: quick help with dummy load

as far as the polarity of the 47uf cap, is the longer leg the pos or neg? and for the in4001 diode the white strip on it? I put this together just like the pics but it doesnt respond the proper way. So I reversed the polarity of the dummy load and it worked as far as measuring the ma's and the volts. Then hooked up the ld and got a small amount of light. Not enough to shine 2 feet on the wall. So i shorted the cap and disconnected the ld and looked at the circuit again. Now i'm lost on what to do.
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Old 02-06-2009, 06:43 PM #4
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Default Re: quick help with dummy load

I have put the dummy load picture in my post above and the circuit diagram in this one...as far as I know they are correct, follow the stripes on the diodes.

Whether your cap is an electrolytic or a tant it should be marked for polarity. Neg is marked by stripe on electrolytics, + normaly printed on tant's.

Quote:
I put this together just like the pics but it doesnt respond the proper way.
I am not sure what you are saying here, could you post a photo of your setup? It may help with diagnosing the problem.

In the mean time, if you connect the dummy load as shown in the top drawing, (red to + black to -), put the meter, set to mv, across the resistor (wire colours not important) when you turn the pot does anything happen?

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quick help with dummy load-lm317_components01_009.jpg  
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Old 02-06-2009, 06:52 PM #5
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Default Re: quick help with dummy load

double post to get the test drawing up : Just a note... I never noticed that in this drawing the resistor is at one end of the diodes and in the other drawing it is at the other end, it does not matter it works fine either way.
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Old 02-06-2009, 07:28 PM #6
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Default Re: quick help with dummy load

in the diagram it uses 2 10ohm resistors and in the tutorial it mentions using 2 3.9 ohm. If using 3.90hm resistor should there be 2 or just use 1. I will take a pic, give me a couple of minutes.
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Old 02-06-2009, 07:48 PM #7
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Default Re: quick help with dummy load

here is my dummy load white wire being pos
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Old 02-06-2009, 07:50 PM #8
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Default Re: quick help with dummy load

forgot pic
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Old 02-06-2009, 07:55 PM #9
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Default Re: quick help with dummy load

here is the driver
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Old 02-06-2009, 08:42 PM #10
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Default Re: quick help with dummy load

Quote:
Originally Posted by madleds
here is the driver

i think your capacitors backwards... if that makes a difference
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Old 02-06-2009, 09:31 PM #11
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Default Re: quick help with dummy load

I had it turned the other way at first but I looked at the diagram and the cap polarity showed it as being backwards, so I reversed it. so what about the 2 3.9 ohm resistors. Is that right. and is my dummy load right?
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Old 02-06-2009, 09:45 PM #12
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Default Re: quick help with dummy load

Quote:
Originally Posted by madleds
here is the driver
Your Capacitor is hooked up backwards... the white wire that goes to your Dummy Load
is Positive... 8-)

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Old 02-06-2009, 09:51 PM #13
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Default Re: quick help with dummy load

Cap is backwards as photographed. Grey stripe is negative, other than that it looks fine (cannot be 100% sure as I am guessing that the LM317 is the right way round).

With the 2 resistors you will get about 2 ohms as the min resistance.
Your test load is correct as well....

Have you checked the ref voltage with the test load in place?

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Old 02-06-2009, 09:57 PM #14
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Default Re: quick help with dummy load

ok, I reversed the cap back arond, put the dummy load bak on. here are the results... Resistor is reading in mv is 15.6 and the diodes are reading 2.961 volts. Is this right?
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Old 02-06-2009, 10:02 PM #15
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Default Re: quick help with dummy load

Voltage looks close for a red, what is your input voltage?

you should have a range from top of pot to bottom of pot in mv, can you post it? (top end should be around *625ma with that setup)

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[edit]What red are you wanting to use with this?[/edit]
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Old 02-06-2009, 10:12 PM #16
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Default Re: quick help with dummy load

output from batt lead is 6.22, top pot range is 245.4 and the low is reading 11.6 did this by mv across the resistor.
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